Digital communication receivers must sample an analog waveform and then reliably detect the sampled data. Signals arriving at a receiver are typically corrupted by intersymbol interference (ISI), crosstalk, echo, and other noise. In order to compensate for such channel distortions, communication systems often employ well-known pre-emphasis techniques in the transmitter or equalization techniques in the receiver (or both). On the receiver side, well-known zero equalization or decision-feedback equalization (DFE) techniques (or both) are often employed. Such equalization techniques are widely-used for removing intersymbol interference and other noise. See, for example, R. Gitlin et al., Digital Communication Principles, (Plenum Press, 1992) and E. A. Lee and D. G. Messerschmitt, Digital Communications, (Kluwer Academic Press, 1988), each incorporated by reference herein. Generally, zero equalization techniques employ a high pass filter to compensate for the low pass effect asserted by the channel. The high pass filter can be a continuous or a discrete filter. Decision-feedback equalization utilizes a discrete-time feedback loop that adds a correction signal, which is a function of previously decoded symbol values, to the channel output.
While such pre-emphasis and equalization techniques can effectively compensate for channel distortions, over-compensation can also have a significant impact on performance. Thus, a number of techniques exist for determining when the equalization techniques have sufficiently compensated for the channel distortions. In the case of zero equalization, for example, an error term is typically fed back to adjust the filter coefficients using well-known techniques. In the case of DFE, a convergence criterion is applied that evaluates an error term. Such stopping criteria, however, have been found to require excessive time to converge and is expensive from an implementation perspective. A need therefore exists for improved techniques for determining when the channel compensation techniques have sufficiently compensated for the channel distortions. A further need exists for methods and apparatus for determining one or more parameters of the channel compensation techniques using data eye monitoring.